Many have heard of the plant-and-cut maneuver, or “faking out” an opponent, during athletic events. The player acts as if she is going to the right but quickly and aggressively plants the right foot and immediately reverses her motion and accelerates to the opposite left side. This occurs in soccer, football, and basketball to get by or away from a defender. Unfortunately, a quick direction change such as this is cited as an injury mechanism for noncontact ACL ruptures (Boden et al. 2000; McNair et al. 1990). Movements such as cutting, rotating, and pivoting occur as often as 70% of the time during the active portion of basketball games (Stacoff et al. 1996). It is during these types of motions that anatomically the leg (knee) can fall into a valgus collapse. The closed-chain theory suggests that excessive knee valgus occurs when the leg (thigh) falls into adduction and internal rotation, while the knee (tibia) moves into a position of abduction as the ankle and foot move into eversion during weight-bearing motions.

It is very possible and highly probable that this position is brought about by faulty neuromuscular function, aberrant postural adjustments, or reflex responses (Ford et al. 2005). Neuromuscular control of the lower extremity affects not only the knee but also the entire kinematic chain (the foot, ankle, knee, hip, and trunk). This makes females especially vulnerable because they display patterns of ligament dominance. Ligament dominance theory is a concept initially developed by Andrews and Axe (1985) to describe their analysis of knee ligament instability. Hewett (Hewett et al. 2002) has expanded its use to describe how during sporting activities, an athlete will allow the knee ligaments, rather than the lower extremity musculature, to absorb a significant portion of the ground reaction forces. Muscular dominance theory provides a better option for most athletes because ground reaction forces are absorbed by eccentric control from the lower extremity muscles. The ligament-dominant motor control pattern is seen during cutting or landing when a female athlete allows the ground reaction force to control the direction of motion of the lower extremity. As the ligament accepts an unusually high load of force, the athlete collapses into the position of excessive dynamic valgus, or valgus collapse described earlier.

This collapse has been seen by Malinzak and colleagues (2001) as greater knee valgus angles not only during running but also during sidestep cuts and crossover cuts in female athletes. Females have also been found to have less knee flexion during the stance phase of a sidestep maneuver when compared with males (Malinzak et al. 2001). McLean et al. (1999) found no difference in knee valgus during running but did in regard to increased maximum knee valgus angles during sidestep cuts when compared with male counterparts. Ford and colleagues (2005) assessed unanticipated cutting patterns and found that female athletes had significantly greater knee abduction angles when readying themselves to execute a cutting maneuver when compared with males. This faulty motor pattern could result in injury, as described in Clinical Correlation 19.1. Ford reports that these gender differences in knee abduction angle during dynamic cutting movements, and even when adapting the ready position, suggest that women employ an altered muscular control of the lower extremity in contraction patterns (motor control) of the knee and hip abductors and adductors (Ford et al. 2005). In the ready position the trunk, knees, and hips are slightly flexed so that the stance is widened and the base of support is lowered.